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-;.'. :--<0 0<: C.:1 c.'~ '. ,~ t--..... en INTRODUCTION This report was prepared as a biological evaluation of stocking nonnative, nonsalmonid fish species in the 50-year floodplain of the Upper Colorado River Basin. We believe that the proposed conditions, in their entirety, will provide diverse sportfishing opportunities and enhance recovery of endangered fishes in the upper basin. Most State fish and wildlife agencies are charged with a dual mission: (1) protect, restore, and enhance fish and wildlife populations; and (2) provide diverse, public recreational opportunities, both consumptive and non- consumptive. The Colorado Wildlife Commission directed the Division to provide diverse sportfishing opportunities (i.e., warmwater fishing) to anglers in the western slope region of Colorado, Since this region already provides ample opportunities for coldwater fishing, numerous warmwater ponds from gravel mining along the Colorado River provide an opportunity to diversify the recreational fishery opportunities by developing warmwater sport fisheries, The proposed conditions for stocking in the 50-year floodplain were prepared to address endangered fish recovery and to provide diversity in recreational fishery opportunities in western Colorado. Other proposals to stock nonnative, nonsalmonid fishes within the 50-year floodplain of critical habitat of the endangered fishes in the upper basin will be evaluated on a case-by-case basis. BACKGROUND Alterations of the rivers from the construction of dams and levees have changed the streamflow regime in the Upper Colorado River Basin (LIpper Basin). In addition, 47. nonnative fish species have been introduced into the Upper Basin either intentionally or accidentally. Numerous factors associated with these changes are believed to have an adverse affect on some fish species that are endemic to the Upper Basin, The razorback sucker (Xvrauchen texanus), bony tail (Gila eleqans), humpback chub (Gila ~), and Colorado squawfish (Ptvchocheilus lucius) are presently classified as endangered under the Endangered Species Act. Although these fishes are long-lived and reproduce successfully, recruitment (i.e., survial to adults) of these fishes has been drastically curtailed. Extremely low or no survival during the early life stages of these endangered fishes limits their recruitment. While various factors are involved, predation and competition by nonnative fish species are believed to cause high mortality of larval and juvenile endangered fishes, thereby reducing recruitment. Gravel deposits in the floodplain of the broad valley sections of the mainstem rivers in the Upper Basin have been mined for use in construction of highways (e.g., Interstate 1-70), foundations of buildings, and other uses. Ponds have been created from these gravel mining operations in the 0- to 50-year floodplain along the Colorado and Gunnison rivers that support warmwater, nonnative fish species. However, escapement of such fish into the rivers